PROJECT SUMMARY Suicide is the second leading cause of death among adolescents in the United States, and nearly 9 percent of high school students report a suicide attempt in the past year. Although distal risk factors for suicide attempts are well established and indicate which adolescents are more likely to attempt suicide at some unknown point in time, previous research has failed to determine warning signs for near-term risk. This is despite the fact that understanding imminent or near-term risk, making a helpful response and intervention possible, is the major challenge facing clinicians, parents and educators who care for adolescents at risk. Addressing this gap in our knowledge has been highlighted as a priority by the National Action Alliance for Suicide Prevention. In this study we propose to identify the 24-hour warning signs for suicide attempts in a national cohort of adolescents. We will prospectively follow 1800 adolescents at elevated risk for suicide from the 14-site study, Emergency Department Screen for Teens at Risk for Suicide (ED-STARS, U01MH104311). These adolescents will complete bi-weekly text message surveys regarding their mental health status across an 18-month period, with existing data indicating that approximately 270 of these adolescents will report a suicide attempt. A detailed computer-assisted telephone follow-up interview, the Warning Signs for Suicide Attempt Interview ? Adolescent, will be conducted with each adolescent who reports a suicide attempt (and matched control adolescents) within approximately one week of the adolescent?s report. We will combine adolescents? baseline data from ED-STARS about distal suicide risk factors (who is at risk) with new data collected in this study about ?when? they are at risk. Using a case-crossover within-subject design, we will compare the events, behaviors, emotions and thoughts of these adolescents during the 24-hour case window (day of attempt) to those during a matched 24-hour control window. Using a case-control group comparison design, we also will identify differences between suicide attempters and non-attempters in events, behaviors, emotions and cognitions during the 24-hour case window. Our primary aims are: (1) to determine 24-hour warning signs for adolescent suicide attempts; (2) to determine whether (and how) 24-hour warning signs differ for subgroups of adolescents with different profiles of distal (baseline) suicide risk factors; and (3) to determine whether baseline scores on a behavioral test of implicit suicide ideation (Suicide-Implicit Association Test) identify a unique subgroup of adolescents at risk for suicide attempt who explicitly deny suicidal thoughts, and if so, whether this subgroup is characterized by a distinct pattern of warning signs. The significance of establishing the warning signs for adolescent suicide attempts is substantial because no previous studies have examined near-term risk for adolescent suicide attempts despite the critical importance of this information. The study has the potential for high impact because study findings could be rapidly disseminated nationally to clinicians, educators and parents of adolescents at risk.